Structure of an exhaust manifold branch collecting portion

Abstract

A collecting portion for an exhaust manifold branch where a combined pipe portion including a plurality of pipes is welded to a collecting pipe wherein, (1) an intermediate member is provided between the combined pipe portion and the collecting pipe, (2) the collecting pipe has a portion that extends upstream, (3) a weld line formed at the downstream end of a partitioning wall is axially zigzagged, (4) a weld line is offset from the downstream surface of the combined pipe portion, (5) only one of the partitioning walls is curved, (6) downstream ends of the partitioning walls are smoothly convex, (7) an additional weld is formed in the partitioning wall, or (8) an intermediate member is welded at a half circumference of the combined pipe portion.

What is claimed is: 
     
       1. An exhaust manifold branch collecting portion structure, said structure being connected to a cylinder head at one end of said structure, said structure comprising: an exhaust manifold including a plurality of pipes having downstream ends, each of said downstream pipe ends having a pie-shaped cross-section having two straight sides and one arc-shaped side, said downstream pipe ends being assembled with the said straight sides of the pie-shaped cross-sections of adjacent downstream pipe ends contacting each other to form partitioning walls and being welded together at downstream ends of said partitioning walls to form a combined pipe portion having a circular cross-section;   a cylindrical intermediate member receiving therein at least a downstream end of said combined pipe portion and welded to said combined pipe portion; and   a collecting pipe having an upstream end receiving therein at least a downstream end of said intermediate member and welded to said intermediate member.   
     
     
       2. A structure according to claim 1, wherein said combined pipe portion of said exhaust manifold and said intermediate member are welded together over an entire circumference of said intermediate member, and said intermediate member and said collecting pipe are welded together over the entire circumference of said intermediate member. 
     
     
       3. A structure according to claim 2, wherein said combined pipe portion of said exhaust manifold and said intermediate member are welded together both at an upstream end of said intermediate member and at a downstream end of said combined pipe portion, and said intermediate member and said collecting pipe are welded together at an upstream end of said collecting pipe. 
     
     
       4. A structure according to claim 1, wherein said intermediate member and said collecting pipe are welded together over an entire circumference of said intermediate member, at an upstream end of said collecting pipe.